2. Forces of Nature
Sir Issac Newton,
“Force is the external agency applied on a
body to change its state of rest and motion”
◦ Gravitational force
◦ Electromagnetic force
◦ Strong nuclear force
◦ Weak nuclear force
3. Length
t Mass
Time
Electric current
Fundamental
Quantity Temperature
Luminous
Intensity
Physical Quantity Amount of
substance
Plane angle
Solid angle
Derived Quantity Area, Volume,
Density
4. S.NO POWER PREFIX ABBREVIATION
OF TEN
1 10-15 Femto f
2 10-12 Pico p
Expressin 3
4
10-9
10-6
Nano
Micro
n
μ
g Larger 5 10-3 Milli m
And 6
7
10-2
10-1
Centi
Deci
c
d
Smaller 8 101 Deca da
Physical 9
10
102
103
Hecto
Kilo
h
k
Quantities 11 106 Mege M
12 109 Giga G
13 1012 Tera T
14 1015 peta P
5. LIGHT YEAR AND ASTRONOMICAL UNIT
Light Year
It is the distance travelled by light in one
year in vaccum.
1 Light Year = 9.467 x 1015m
Astronomical unit
It is the mean distance of the centre of
the sun from the centre of the Earth.
1 Astronomical Unit (AU) = 1.496 X
1011m
6. Determinationof Distance
Laser pulse method
Determination of mass
Determinationof time
Atomic clocks – 1013 sec
Quartz clocks – 109 sec
7. Significant figures
The number of meaning digits in a number is called
the number of significant figures.
RULES
1. All the non- zero digits in a number are significant.
2. All the zeros between two non-zeros digits are
significant, irrespective of the decimal point.
3. The zeros at the end without a decimal point are not
significant.
4. The trailing zeros in a number with a decimal point
are significant
8. Significant Figures Examples
0.0631 – Three Significant Figures.
56700 - Three Significant Figures.
0.00123 – Three Significant Figures.
30.00 – Four Significant Figures.
6.320 – Four Significant Figures.
600900 – Four Significant Figures.
346.56 – Five Significant Figures
5212.0 – Five Significant Figures.
9. Rounding Off
If the insignificant digit is more than 5,
◦ The preceding digit is raised by 1.
If the insignificant digit is not more than 5,
◦ There is no change.
If the insignificant digit is 5
◦ Even
there is no change.
◦ Odd
The preceding digit is raised by 1.
11. Errors in Measurement
♣ Constant Errors
It is due to faulty calibration of the scale in the measuring
instrument.
♣ Systematic Errors
These are errors which occur due to a certain pattern or system.
♣ Gross Errors
a. Improper setting of the instrument.
b. Wrong recording of the observation.
c. Not taking into account sources of error and precautions.
d. Usage of wrong values I the calculation.
♣ Random Errors
It is very common that repeated measurement of a quantitative
values which are slightly different from each other.
12. Dimensional Analysis
Dimensions of a physical quantity are the powers to which the
fundamental quantities must be raised.
Fundamental Quantity Dimension
Length L
Mass M
Time T
Temperature K
Electric current A
Luminous intensity cd
Amount of substance mol
13. Dimensional Quantities
◦ Dimensional variables are those physical quantities which
possess dimensions but do not have a fixed value.
Ex. Velocity, force, etc.,
Dimensionless Quantities
◦ There are certain quantities which do not possess dimension .
Ex. Strain, angle, specific gravity, etc.,
Principle of homogeneity of dimensions
◦ An equation is dimensionally correct if the dimensions of the
various terms on either side of the equation are the same.
Ex. A+ B = C is valid only if the dimensions of A, B & C are the
same.
14. Uses of Dimensional Analysis
Convert a physical quantity from one
system of units to another.
Check the dimensional correctness of a
given equation.
Establish a relationship between different
physical quantities in an equation.
15. Limitations of Dimensional
Analysis
The value of dimensionless constants cannot be
determined by this method.
This method cannot be applied to equations involving
exponential and trigonometric functions.
It cannot be applied to an equation involving more
than three physical quantities.
It can check only whether a physical relation is
dimensionally correct or not. It cannot tell whether the
relation is absolutely correct or not.
